diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-utils.c
index 5e571955b6..a40d81219c 100644
--- a/hw/cxl/cxl-mailbox-utils.c
+++ b/hw/cxl/cxl-mailbox-utils.c
@@ -151,6 +151,9 @@ static CXLRetCode cmd_tunnel_management_cmd(const struct cxl_cmd *cmd,
     in = (void *)payload_in;
     out = (void *)payload_out;
 
+    if (len_in < sizeof(*in)) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
     /* Enough room for minimum sized message - no payload */
     if (in->size < sizeof(in->ccimessage)) {
         return CXL_MBOX_INVALID_PAYLOAD_LENGTH;